Violence could spread across the Middle East with Israel paying a "heavy price" if it launched military action against Iran, the deputy leader of Hezbollah said on Thursday.

"Israel or the United States cannot just bomb Iran and (expect) things to continue normally," Sheikh Naim Qassem told Reuters. "Any attack on Iran could ignite the whole region and the assailant will pay a heavy price whether it's Israel or the United States."

He said any countries which allowed an attack on Iran to be launched from US bases on their territory would also face reprisals.

Qassem refused to discuss details of Hezbollah's role in responding to any attack on Iran.

Israeli officials say Hezbollah, and to a lesser degree Hamas, would launch cross-border rocket salvoes on Iran's behalf should it come under attack and this scenario was featured in an Israeli-US air defense exercise last year.

Earlier this month, the United Nations special coordinator for Lebanon expressed concern that a wave of bellicose rhetoric between Israel and Lebanon has fuelled fears the two hostile neighbors could be headed for another conflict.

Lebanese and Syrian officials have accused Israel of pushing for a new war in the Middle East but Qassem said he did not expect a war soon.

"Based on our expectations ... there are no signs for a war soon, but Israel is planning for one and whether this day is far or near we have to be ready and prepared and that is what we are now," he said.